The present invention relates to servo driven valves and particularly to valves of the type employed for controlling flow of water or engine coolant to a heat exchanger for an occupied space such as the passenger compartment of a vehicle. Valves employed for passenger compartment heat exchangers or heater cores as they are often called are commonly of the butterfly vane type and heretofore the butterfly has been operated by a servo motor typically of the type employing a vacuum operated diaphragm connected via a linkage to the butterfly shaft.
Automotive heater core valves of the aforesaid type have the disadvantage that a source of vacuum is required to be supplied to the location of the vacuum motor for the valve; and, where it is desired to provide a heater core in the rear of a bus or passenger van, it is necessary to route vacuum lines for a substantial distance. Where a heater core valve is located in a position requiring long vacuum lines, the potential exists for breakage in the lines and leakage which would render the vacuum motor inoperative. Accordingly, it has been desired to replace vacuum motor operated heater core valves with electrically operated valves which eliminate the need for lengthy routing of vacuum lines. However, it has been proven costly in terms of the volumes encountered in mass production of automobiles to provide for an electrically operated servo driven water valve for a heater core in view of the cost of providing a means for sensing the position of the valve for generating a feedback signal to enable precise control of the valve position.
In certain applications, it has been desired to provide an electrically operated servo driven heater core water valve which operated only in one of two positions, e.g., either fully open or fully closed thereby eliminating the need for a valve position feedback signal. Where such a simple servo driven valve operation is desired, it has nevertheless proven difficult to provide a way or means of sensing the fully open or fully closed valve position and stopping the motor drive to the valve without employing costly plural travel limit switches or electronic or electrical means for sensing motor current or other parameters to determine the point at which the motor should be de-energized.
Thus it has long been desired to provide a way or means of providing an electrically operated two-position servo actuator which could be manufactured inexpensively in high volume mass production for automotive applications and which automatically cuts off the drive motor when the limit position is reached without the need for costly electronics, yet one vehicle could be pre-energized upon command by a single means.